The obective of this study is to test the hypothesis that a simulation technique can be used to develop criteria for diagnosing infraction in patients with conduction system defects, specifically, right in left bundle branch block, superior and inferior hemiblocks of the left bundle. Through an extensive use of a mathematical-physical simulation of the electrical field produced by the heart, criteria can be established to remove the uncertainty and confusion in ECGs and VCGs produced by combined infarction and conduction abnormality and to define more clearly those situations where confounding still remains. Methods validating the simulation involve a mathematical fitting of human VCGs with simulated VCGs and then comparing the epicardial map taken from the patient to the epicardial map computed from a wave-propagation simulation used to generate the VCG. The method of simulation is based on a cmplete mathematical model of the physical problem and inclues all major influences in the genesis of the surface electrocardiogram. The cardiac generator portion of the simulation includes the heart size and shape, conduction and Purkinje systems, and pathway of ventricular depolarization. After the cardiac generator has been simulated, it is then processed through a simulation of the torso containing the major inhomogeneities to produce the body surface electrocardiogram. The cardiac generator simulation is a numerical solution to the problem of simulating the pathway of ventricular depolarization in a way analogous to Huygen"s geometric method of wavefront construction. For the torso simulations we have been using the Gelernter-Swihart method which is a mathematical-physical model relating in a quantitative way the electrical activity within the heart to the complete time-varying potential distribution at the body surface. One of the long-range objectives is to perfect this simulation to the point where it becomes the basis for experiments in electrocardiography.